D interface bug?

[destructionator at gmail.com]

On Friday, 29 March 2019 at 23:44:35 UTC, Alex wrote:
> interface iBase
> {
> 	iBase fooBase(iBase);
> }
>
>
> class cBase : iBase
> {
> 	cBase fooBase(cBase c) { return c; }	
>
> }
>
> cBase.fooBase should be a valid override of iBase.fooBase 
> because
>  they are the same type!

The return value there is allowed, but the parameter is not. Consider this case:

class AnotherChild : iBase { /* snip */ }

iBase i = new cBase(); // allowed, cBase implements iBase
i.fooBase(new AnotherChild);


That second line should be allowed: the interface says it accepts any implementation of the iBase interface.

But the cBase implementation doen't allow *any* implementation of iBase - it only accepts cBase and down. That function wouldn't be able to handle my AnotherChild instance.

Thus, cBase.fooBase does NOT implement the iBase's interface, and it fails to compile.